Degradable organic acids for extraction of As, Cr and Cu from contaminated soils

Start date:
Jun 26th, 2014

Finish date:
May 18th, 2016

The potential for simultaneous extraction of metalloids and heavy metals from contaminated soil by the degradable agents oxalate and citrate was investigated by batch experiments over 24 hours. The investigated soil was the fine fraction (< 62 μm) from a Danish CCA contaminated soil collected at the Collstrop site. The fine fraction contained total As, Cr and Cu concentration of 1.155, 309 and750 mg/kg.

Oxalate shows a high potential for simultaneous extraction of As, Cr and Cu from the fine fraction. The maximum extraction efficiency was 75, 28 and 85% of the total soil concentration for As, Cr and Cu, respectively. Citrate shows equally good results for Cr and Cu with removal efficiencies of 25 and 82%, respectively. However, citrate was much less effective for removal of As and only showed an extraction efficiency of 41%.

The extraction efficiency of oxalate was negatively influenced by an increase in pH especially for As. A pH of 5.5 and an oxalate concentration of 0.25 M or higher is recommended for simultaneous remediation of As, Cr and Cu. The liquid:solid ratio should be 10 and two repeated extractions have to be carried out to obtain the optimal extraction.

These results showed that oxalate is a very potent extraction agent for simultaneous remediation of metalloids and heavy metals from contaminated soils. Since oxalate is easily degradable its use should not pose any threat to the environment.